As a sintered sliding member exposed to a high-temperature exhaust gas, there has been known a bearing used in a recirculated exhaust gas flow rate regulating valve of an EGR (Exhaust Gas Recirculation) type internal-combustion engine (Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-521610). Particularly, as a bearing used in the recirculated exhaust gas flow rate regulating valve of the EGR type internal-combustion engine, there have been known: a bearing made of graphite; and a bearing made of a sintered Cu alloy containing 7-10% Sn and 5-9% C by mass.
However, the internal-combustion engine has been made dramatically high-powered and fuel-efficient in recent years. Further, it has been strongly required that the internal-combustion engine be made lighter and more compact. For this reason, the aforementioned recirculated exhaust gas flow rate regulating valve is now more often than not provided in the vicinity of a combustion chamber of the engine. As a result, it is assumed that the recirculated exhaust gas flow rate regulating valve is now disposed in a high-temperature environment of 500-600° C. in association with an increasing heat generated by the high-powered engine.
As a bearing that can be used in such a high-temperature environment, Japanese Unexamined Patent Application Publication No. 2004-68074 discloses a bearing made of a sintered Cu alloy containing: 10-30% Ni, 5-12% Sn and 3-10% C by mass; and a remainder composed of Cu and unavoidable impurities. Such sintered Cu alloy has a structure in which free graphite is dispersed in a Cu—Ni—Sn-based solid solution serving as a basis material.
Meanwhile, examples of sintered sliding members exposed to seawater or a snow melting agent, include: a sliding member for use in an outboard motor; and a bearing of an exhaust throttle valve used in a diesel exhaust emission purification system. It is required that these members exhibit high corrosion resistance. Particularly, the bearing of the exhaust throttle valve is required to exhibit thermal resistance, corrosion resistance and wear resistance, when heated by a high-temperature chloride and cooled, in a repeated manner. In fact, this bearing is a stainless-steel member.